Electromagnetic wave direction indicator



April 26, 1949. R. HARDY ELECTROMAGNETIC WAVE DIRECTION INDICATOR FiledMay 28, 1943 2 Sheets-Sheet 1 1 2 LOH FREQl/E/VCY I may 4/vo Mia/Monzcron oar/ 07 AMPZ/F/t'k 4 mm (awry AMP; mm,

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29 J4 F Q (L I I Q Q J nae lm zwmn RENE HHRD Y ATIDRNEY Patented Apr.26, 1949 ELEGTROMAGNETIC WAVE DIRECTION. INDICATOR Ren Hardy, Lyon,France, assignor to International Standard Electric Corporation, New

York, N. Y.

Application May 28, 1943, Serial No. 488,876

In France April 18, 1941 Section 1, Public Law 690, August 8, 1946Patent expires April 18, 1961 9 Claims. (Cl. 343 -118) The presentinvention relates to electroma netic waves direction indicating systemsand is an improvement over the system disclosed in my copending patent.application filedMay 28, 1943, Ser. No. 488 875, now Patent No.2,440,268 issued April 27, 1948.

The direct reading radio direction finder circuits described in theabove mentioned application comprise means for eliminating the 180inaccuracy in the direction of the indications obtained by eliminatingthe wrong direction portion of the image produced on the screen of thecathode ray tube used as an indicator. For this purpose, these circuitscomprise a device generating short pulses, for example a thyratronrelaxation circuit. which is synchronized by the detected envelope curveof the received signals and which at each pulse switches in a verticalantenna or doubt remover circuit. The short duration currents thusfurnished by the doubt remover-circuit are added and cut ofl alternatelyfrom the detected envelope curve, and the current peaks resulting fromthe addition of the doubt remover current to the current of the receivedsignals serve to block the cathode beam during part of the scanningthrough biasing of tube and permitting the use of usual control circuitsfor this tube.

Also, the present invention has likewise among itsobjects to providemeans for assuring, in such circuits, the repetition at a distance ofthe radio direction finding indications.

According to certain features of the present invention, means permittingthe cathode spot to be extinguished during the desired portion of thescanning and comprising the pulse-generating in amplitude bythe'detected envelope curve and the control grid of the cathode raytube, the

duration of the blocking being adjusted to about half of the duration ofthe scanning by'a suitable time constant circuit.

It is not however always possible thus to control the grid of a cathoderay tube, particularly when tubes are used in which the luminousintensity of the spot is adjusted by an auxiliary anode. Further, theprocess as described in the above mentioned application requires amodification of the cathode ray tube circuits that might not bedesirable for proper operation of the tube.

Moreover, the application to the grid of the cathode ray tube of anunbalanced voltage such as obtained by the combination of doubt removerpulses and the detected current of the received signals might lead to aself-biasing of the grid the eflect of which is to give to this grid amean biasing varying with the importance of the signal modulating it andconsequently causing variation of the luminous intensity of the spotduring the time it remains visible.

Consequently, the present invention has among its objects to provideradio direction finding indicator circuits assuring elimination of the180 inaccuracy in the direction of the indications in the mannerdescribed in the said application but not involving fluctuations of theluminosity of the image visible on the screen of the cathode ray theoutput of which thus modulated and interrupted is transmitted to atransmission line to be applied to one or more distant cathode ray tubesso as to cause a direction finding indication to appear there withoutdirection inaccuracy.

' These objects and features," as well as still others, will beexplained in detail in the following description given with reference tothe accompanying drawings,inwhich:

Fig. 1 shows schematically a radio direction finder circuitincorporating features of the invention;

Fig. 2 shows a group of curves used in the description;

Fig. 3 shows a type of indication that can be obtained with the circuitshown in Fig. 1; and

Fig. 4 shows a radio direction finder circuit comprising means forrepeating the indications at a distance in accordance with features ofthe invention.

Figure 5 shows a wiring diagram of a thyratron doubt remover circuit fora radio direction finder.

In Fig. 1 is shown an example of a radio direction finder circuitembodying features of the invention, in the case where the indication isobtained by circular scanning in the indicating cathode ray tube. Itshould be understood however that the invention can be applied to everymanner of scanning and to every type of radio direction indicationdesired.

In the example shown, the crossed wave collecting loops, or directionalreceiving aerials of any other suitabletype, are assumed to be connestedat I and 2 across stators 3 and l of a direction flnder of usual typewhose rotor I supplies the input or a receiver comprising high andmedium frequency stages 6, a detector stage I and a low frequency outputampliiler tube or stage 8. Detector I controls the grid of output stageI. These circuits, as well as the other circuits the structures of whichdo not require a detailed description and which may be well known inthemselves, are shown simply as rectangles.

In the output circuit of low frequency stage 8 is connected aninductance 9 that rotates around cathode ray tube ll, so as to ensurethe driving in continuous and uniform rotation of the cathode beam ofthis tube, and hence of cathode spot II in a circle, such as shown bydotted lines at So long as the aerials receive no signal, output.

stage 8 has a constant plate current of a value determined by thebiasing of its control grid. and spot II is driven in rotation alongcircle l2, as described. As soon as a signal is received by the aerials,after reception of this signal and amplification in detector I, theplate current of output stage .8 is modulated and the spot is shiftedradially from its circular trajectory.

The input circuit of the receiver likewise is supplied by a doubtremover circuit Hi. This doubt remover circuit can have any well-knownarrangement and is supplied by vertical or alldirectional antenna I'I.Its output circuit comprises means for bringing high frequency voltagescoming from antenna I! to the input of the receiver with a suitablephase so as to be able to superimpose them on the high frequencyvoltages coming from the directional antennas with a suitable amplitude.When this doubt remover stage I! is connected efiectively to thereceiver, it superlmposes in phase or in phase opposition avoltage ofconstant amplitude on that coming from rotor 5 of the finder.

According to a feature 01' the invention, this doubt remover stage isbrought into eflective is obtained showing maxima and minima. Thismodulated voltage serves to synchronize the discharge of the thyratronwhich is then brought into operation. During the very short timecorresponding to the discharge, the thyratron unblocks doubt removerstage I which, during that very short time. applies to the input of thereceiver a high frequency voltage coming from antenna IT, in phase or inphase opposition, successively at each half turn of the rotor. withrespect to the voltage coming from rotor 5. A buifer or amplifiercircuit I may be provided between the detector 13 and relay circuit ii.

The operation of the system will appear clearly by referring to Fig. 2:In curve A is shown at 20 and 21 the envelope curve detected from theradio direction finder for a full turn of rotor 5 of. this iinder. Thiscurve consists of two juxtaposed half-sinusoids whose maxima 25 and 21serve to synchronize discharges 26 and 28 of thyratron relay llgivingtoothed voltages 22, 23, 24, etc.', shown in curve B. During the shortmoment of the discharge of the thyratron, the sudden variation ofvoltages produced is used to unblock doubt remover stage II. This stagethen generates short voltage pulses that are added algebraicallyaccording to their phase todetected curve 20, 2| in the manner indicatedin curve C of Fig. 2. In fact, during one half-turn, the current comingfrom vertical antenna I1 is in phase with thecurrent' arriving fromrotor 5 of the finder, and "positive peak II is obtained athalt-sinusoid 2!, and for the other half-turn the doubt remover currentis in phase opposition, hence is translated into the appearance of anegative" peaks 32 at half-sinusoid Ill.

Curve C thus does not exceed an amplitude 33 except once for each iullturn at the moment of positive peak 2!. This amplitude peak can be usedin a time constant circuit of any known suitable structure I! to furnisha voltage such as voltage 34 of curve D of adjustable duration 36. Thisadjustable duration voltage 36 serves to control the extinction of thespot of the cathode ray tube ll through blocking of output stage 8 ofthe receiver. The voltage produced by time constant circuit II is usedfor the negative biasing of output stage I in series with detectorcircuit 1 so that there be no plate current in stage I during a timeinterval 36 rendered for example equal to one half-period of detectedoperation only during very short time intervals,

as already described in the application above referred to. A relaycircuit, for example a thyratron circuit I5, is used to control itsoperation. An example of the arrangement of such a circuit is disclosedin the said application and is shown in Fig. 5. The arrangement includesa thyratron 12 with a condenser 13 connected in its platecathodecircuit. The cathode circuit includes the plate-cathode circuit of aconstant current pentode H. When the thyratron is oil? the condensercharges at a constant rate through the pentode; when the thyratron isturned onlby a signal from the amplifier I4 applied to its grid, itdischarges the condenser producing the rectangular voltage pulse on its.plate. The

- thyratron is at rest when no signal is detected in a detector circuitl3 connected in shunt with detector I at the output of high and mediumfrequency stages 6 of the receiver. However,

as soon as a signal is received by the directional antennas andamplified at 6. owing to the rotation of rotor 5 of the finder, anenvelope-curve envelope 2H! from amplitude peak 3| to inverse directionamplitude peak 32. The use of the voltage of circuit ll as biasing foroutput stage 8 is made possible by means of a suitable circuit I!comprising, for example, a tube biased not far from the cut oi! of itsplate current or else a high frequency oscillatory circuit whoseamplitude variation is controlled when the voltage of time constantcircuit II exceeds value 35, curve D, or any other suitable arrangementfor giving output stage I a neg tive bias blocking its plate current ateach inerval 36.

In this way, the spot of cathode ray tube ill will remain in the centeof screen 31 of the tube, Fig. 3, while the ne ative bias applied tooutput stage 8 will be such that there will be no longer plate current.The spot, which in the absence of signal describes circle II on screen31, normally traces, without doubt remover circuit, an image such as I,ll and this image does not allow determining directly whether thedirection of the received emission is il'or'fl. Time constant circuit llgiving voltage 34 per- -mits of maintaining the spot in the center of toany other system for indication or deviation 7 of the spot on the screenof the cathode ray indicator. Thus, for example, the fact of acting uponthe grid of the output stage of the amplifier and no ionger upon thecontrol grid of the oathode ray tube permits of using a rotatingpotentiometer instead of an inductance mechanically displaced around thetube, which hence allows a complete mechanical separation between theradio direction finder and the indicator. Any mode of scanning and ofdeformation of said scanning for creating an indication can be usedlikewise instead of the circular scanning described.

Likewise, it is possible to use the output voltage of stage 8 tomodulate a carrier current, which can then serve to transmit to adistance the radio direction finding indication, whereas if the grid01'. the indicator tube were modulated it would be necessary to use asupplementary transmission. An example ofsuch a system for repeating ata distance the radiodirection finding indication is shown schematicallyin Fig. 4.

In Fig. 4, the various circuits elements, being of a form already knownor described, are not aeaoee plate current oi the modulator tube by asum ciently strong detected signal.

As described with reference to Figs. 1 to 3, a radio direction findingimage can be obtained on the screen of the cathode ray tube by shiftingthe spot towards the center of the screen through the diminution of theplate current of a tube modulating the scanning voltages applied to saidfirst tube. The spot is in the center when there is no longer platecurrent in the modulator tube, and through the blocking of this tube itcan be kept there (lining the desired portion of each scanning. In thesystem shown in Fig. 4, this blocking is obtained by means of timeconstant .circuit 62 which suppresses the output current of transmitter63 during the useless portion of the scanning produced by the carriercurrent in the windings of a two-phase distributor 65, consisting, forexample, of an inversed radio direction finder whose rotor is driven insynchronism with shown in detail. Loops 5i and. 52 indicate adirectional antenna system, which can be of any suitable type, and areconnected to a radio direction finder 53 whose rotor driven by motor 54supplies the high and medium frequency circuits of receiver 55. Thesehigh and medium frequency circuits are followed by a detector circuit 56and by a low frequency circuit 51 intended for listening, for example,its output supplying a pair of phones or a loud-speaker (not shown). Arelaxation circuit, for example, a thyratron circuit 60 is synchronized,asindicated, by connection 6| by means of the envelope curve of thecurrent detected in circuit 56, and the discharge of this thyratron orother synchronized relay permits of bringing into operation, for a veryshort time, doubt remover circuit 58 which puts in phase or in phaseopposition the high frequency current coming from vertical antenna 59 tothe that of finder 53 by motor 54.

The two stators of distributor 65 are connected to transmission lines 68and 69 to which different local cathode indicators and receivers can beconnected. At the near end of transmission lines 56 and 69 can beconnected, for example, a local tell-tale equipment comprising areceiver 66 and a cathode ray indicator 61. At the far end oftransmission lines 68-69 is shown in Fig. 4 and equipmentcomprising areceiver HI and a cathode ray indicator II where appears the same imageas at indicator 61. The two-phase high frequency voltages distributedover transmission lines 68-69 are detected in receivers 66 and 10 andsupply cathode ray tubes 61 and II During the useless portion of theimage, for example, that comprised in sector 42, Fig. 3, the cathodespot will be kept in the center of the screen. no

input of high frequency circuits of the re- 0 as those shown at 3| and32 in curveC of Fig. 2.

These peaks are used in an adjustable time concarrier current being thentransmitted to twophase distributor 65. The other portion of the image,which will appear at both indicators, will give the desired indicationof direction and sense.

It is evident that the-invention is not limited to the embodimentexamples shown and described, but rather is capable of numerousmodifications and adaptations without exceeding its stant circuit 62 toobtain a voltage of an amplitude and of a duration suitable foreliminating or modifying the operation of another circuit provided todistort the amplifier modulation current.

In the arrangement shown, the output of time constant circuit 62controls suitably, as indicated by connection 64, the modulating portionof a conventional carrier current transmitter of relatively highfrequency, 100 kilocycles for example.

On the other hand, the envelope curve coming from detector circuit 56serves to modulate, in known manner, the amplitude of the carriercurrent generated by transmitter 63. The operating point of themodulator tube of carrier current transmitter 63 is adjusted so that inthe absence scope.

I claim:

1. A radio direction finder comprising a directional antenna, means torotate the directivity of saidantenna, means to receive a signal fromsaid antenna, means to detect said signal, means to produce pulses fromportions of said detected signal having a value above a predeterminedvalue, an omnidirectional antenna, means controlled by said pulses tofeed signals from said last mentioned antenna into said receiving meansduring the periods of said pulses only, a cathode ray tube, means tocontrol the spot of said tube in one coordinate of a two coordinatesystem in accordance with the rotation of said antenna directivity,means to control said spot in the other coordinate by the output of saiddetecting means, and means to move said spot to a predetermined positionfor a prdetermined time when the output of said detecting means risesabove a predeter-- mined value by preventing the output of said .tionalantenna, means detecting means from controlling said spot in said othercoordinate,"

2. A radio direction finder in accordance with claim 1, in which the twocoordinates are polar coordinates. a

3. A radio direction flnder in accordancewith claim 1, in which themeans tomove the spot on the cathode ray tube to a predeterminedposition when the output of the detecting means rises above a,predetermined'value comprises a time constant circuit connected to blockout the signal delivered from said detector to said cathode ray tube.

4. A radio direction finder in accordance with claim 1, in which themeans to move the spot onv the cathode ray tube to a predeterminedposition includes a time constant circuit to hold vsaid spot in saidposition for approximately one half the rotation oi. the directivity oithe directional antenna.

5. A radio direction finder in accordance with claim 1, in which thecoordinate system for controlling the spot of the cathode ray tube is apolar coordinate system. and in which the spot is moved to the center 01the system when the output of the detecting means rises above apredetermined value. i

6. A radio direction finder comprising a directoyrotate the directivityof said antenna, a receiver including selector and amplifier circuitsconnected to said antenna, a detector connected to said receiver fordetecting the low frequency envelope of the output of said receiver, apulse generating circuit connected to the output of said detector andadapted to produce pulses in synchronism with the peaks of the detectedenvelope, an omnidirectional antenna,

for said other coordinate oi indication for a portlon o! the cycle ctrotation of said directivity of said directional antenna.

7. A radio direction finder comprising a directional antenna. means torotate the directivity of said antenna, means to receive a signal fromsaid antenna, means to detect said signal, means to produce pulses fromportions of said detected signal having a value above a predeterminedvalue, an omnidirectional antenna, means controlled by said pulses tofeed signals from said last mentioned antenna into said receiving meansduring the periods of said pulses only, a transmitter, means to modulatethe high frequency of said transmitter by the output or said detectingmeans, means to reduce the high frequency oi. saidtransmittersubstantially to zero during predetermined means controlled by saidpulses to connect said omnidirectional antenna to said receiver duringthe periods of said pulses whereby alternate half cycles of the outputof said detector are provided with increased voltage peaks, anindicating device arranged for indication in two coordinates, means tocontrol one of the coordinates of indication of said indicating deviceby the rotation of said directivity of said directional antenna, meansto control the other coordinate of indication by the output of saiddetector, and'means to cause said voltage peaks to block out the effectof the output of the detector on said controlling means Number periodsor time by said pulses, a pair or output channels for said auxiliarytransmitter, means to cause the output of said transmitter in said twochannels to be in phase quadrature, means to vary the amplitude of thesignal in said two channels in synchronism with the rotational of saiddirectivity. of said antenna, the amplitude in said pair of channelsbeing varied inversely, an indicating device located at a remote point,and means to utilize the voltages in said two channels to produce anindication oi direction and sense on said indicating device.

8. A'radio direction finder in accordance with claim '7, in which themeans to cause the signal in the two channels from the transmitter to bein phase quadrature is algoniorneter in which the two channels areconnected to the two stator coils,

. the output of the transmitter is connected to the rotor coil, and therotor coil is turned in synchronism with the directivity ofthe antenna.

9. A radio direction ilnder in accordance with claim 7, in which theindicating' device at the remote point is a cathode ray tube.

' RENE HARDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED s'ra'ms rams-rs Name Date 2,263,377 Busignies et al. Nov. 18,1941 2,27 9,466

Johnske et al. Apr. 14, 1942

